Dry etch stop process for eliminating electrical shorting in MRAM device structures

ABSTRACT

The present invention relates generally to semiconductor fabrication and particularly to fabricating magnetic tunnel junction devices. In particular, this invention relates to a method for using the dielectric layer in tunnel junctions as an etch stop layer to eliminate electrical shorting that can result from the patterning process.

This application is a CIP of Ser. No. 10/937,660 Sep. 9, 2004 U.S. Pat.No. 7,169,623 and claims benefit of 60/783,157 Mar. 16, 2006, entitle“Dry etch stop process for eliminating electrical shorting in MRAMdevice structures”, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor fabrication andparticularly to fabricating device structures containingmetal-insulator-metal layered thin film stacks such as those used inmagnetic tunnel junction devices and memory devices.

BACKGROUND OF THE INVENTION

Layered films of metal-insulator-metal are employed as storage elementsin memory devices such as magnetic random access memories (MRAM) and thelike. The memory element for the MRAM technology is a patternedstructure of multilayer material and is usually composed of a stack ofdifferent materials such as NiFe, CoFe, PtMn, Ru, etc., and may includeinsulator-like materials such as Al₂O₃ or MgO. A typical stack maycontain as many as ten or more layers of these materials some of whichare non-magnetic, some of which are magnetic, and one or two of whichare insulating. The insulating films in this description are defined asoxidized or nitridized metal layers that exhibit high electricalresistance in their bulk form. To fabricate a storage element, it isnecessary to deposit the materials in overlying blanket films, layer bylayer, to form a patterned layer of photoresist, and to etch the filmsinto appropriate structures.

Ion beam milling or ion beam etching processes have been employed toremove magnetoresistive materials. Ion beam milling, however, is aphysical milling process. Areas that are not protected by the mask areremoved by bombardment with ions. The bombardment of ions sputters orpeels away the unprotected material. Ion beam milling operates with lowselectivity, and the portions of the stack that are near to the edges ofthe mask or the boundaries of an MRAM cell body can be easily damaged.

Chemical etching techniques have also been employed to selectivelyremove portions of deposited layers. Examples of etching techniquesinclude dry etching techniques and wet etching techniques.

One of the drawbacks of current etching techniques is that the profilesof MRAM structures are susceptible to electrical shorting across thethin tunnel junction. The vertical separation between the upper magnetlayer above the insulating dielectric tunneling layer and the lowermagnet layer below this tunneling layer is inadequate to preventelectrical shorting.

SUMMARY

Embodiments of the present invention are directed to, among otherthings, fabrication of magnetic tunnel junction (MTJ) devices wherebythe tunnel barrier layer serves as the stop layer during plasmaoveretching of the upper magnetic layer. The resulting MTJ devicesexhibit superior electrical isolation across the tunnel barrier layer.

In another embodiment, the gases employed during plasma overetchingpreferably excludes halogen containing species which result in highlyselective etching of the upper magnetic layer vis-à-vis the tunnelbarrier layer. The introduction of oxygen in the gas enhances thereproducibility of the process.

In yet another embodiment, a fluorine-chlorine gas mixture is employedto partially etch the magnet layer over the tunnel barrier layer.

Finally, another embodiment is directed to corrosion plasma treatmentwith He and H₂ gas prior to or during the stripping of the photoresistmask. Optionally, rinsing with water and He and H₂ dehydration bakingcan be employed following the stripping step.

DESCRIPTION OF THE DRAWINGS

FIG. 1. Typical MRAM structure with magnetic tunneling junction.

FIG. 2. Simplified MRAM structure with magnetic tunneling junction

FIG. 3. Inventive MRAM process sequence

FIG. 4. Inventive MRAM process sequence

FIG. 5 a. Inventive MRAM process sequence

FIG. 5 b. Inventive MRAM process sequence

FIG. 6. MRAM stack structure after top contact patterning

FIG. 7. MRAM stack structure after reactive magnet-layer etch step

FIG. 8. MRAM stack structure after reactive magnet-layer etch

FIG. 9. Embodiment of the inventive MRAM patterning sequence in whichthe tunneling dielectric layer is not breached in the vicinity of thefeature but is breached in areas not in close proximity to the maskfeature

FIG. 10. Embodiment of the inventive MRAM patterning sequence in whichthe magnetic stack layers are intentionally etched with a sloped profileduring a reactive etch step prior to the etch stop process

FIG. 11. Plot of optical emission signal intensity obtained during theetch of a 50 Å NiFe/15 Å alumina/50 Å NiFe stack structure. The twopeaks in the plot indicate the removal of the two NiFe layers. The timebetween the two peaks indicate the time required to remove the 15 Åalumina layer. The NiFe-to-alumina etch selectivity obtained from theprocess used to produce the graph is greater than 90:1.

FIG. 12. Graph of etch sputter rates for CoFe, NiFe, and alumina.

FIG. 13. MRAM stack structure after reactive magnet layer etch (see FIG.6) and etch stop process

FIG. 14. MRAM stack structure after reactive magnet layer etch (see FIG.7) and etch stop process

FIG. 15. MRAM stack structure after reactive magnet layer etch (see FIG.8) and etch stop process

DESCRIPTION OF THE INVENTION

The present invention is based, in part, on the development of apatterning method for fabricating magnetic tunnel junction (MTJ) devicesthat are employed in magnetic random access memory (MRAM) devices. Asfurther described herein, a critical aspect of the invention is that MTJdevices prepared by the inventive process afford superior electricalisolation between the magnet layers in contact with the dielectrictunnel layer in comparison to the current art.

A typical MRAM structure, within which an MTJ is contained, is shown inFIG. 1. The MRAM structure is a complex stack of magnetic, conductive,and insulating films on a substrate. In FIG. 1, the specific componentsof a typical MRAM structure are shown and consist of a substrate 10, abarrier layer 12, a bottom contact layer 14, a mulitlayer fixed magnetstructure 16 consisting of layers of CoFe, Ru, NiFe, IrMn, PtMn, and thelike, a dielectric tunnel layer such as alumina or MgO 18, a switchablemagnet layer 20 (NiFe, CoFe, CoNiFe, CoFeB, and the like), and a topcontact layer 22 (Ta, TaN, Ti, TiN, W, and the like).

Also shown in FIG. 1 is a hard mask layer 24, an antireflective coating26, and a patterned layer of photoresist 28. Photoresist layer 28 is alight sensitive material that is commonly used by those skilled in theart of electrical device fabrication as a mask to etch one or more ofthe underlying layers below the photoresist so that portions of theunderlying layer not protected by the resist layer can be etched away.Antireflection coating 26, which is typically 300 Å to 800 Å thick, iscommonly used to absorb radiation to form an optically opaque film toenhance the contrast of the imaging resist. ARC coatings effectivelyreduce reflection of the incident radiation back into the overlying PRmask layer. This prevents overexposure of the photoresist material. Hardmask layer 24 is commonly used in device fabrication as an intermediatemask transfer layer. When utilized, the photoresist is used as a dryetch mask to transfer the pattern into the hard mask, and possibly oneor more of the underlayers, after which the hard mask layer is used as amask to transfer the pattern into the remaining underlayers that are notdefined using the photoresist. Hard masks such as silicon dioxide andsilicon nitride are commonly used as a means to improve the durabilityof the mask relative to that of photoresist or to allow processing attemperatures above the softening point of polymeric photoresist layers.

Magnetic stack structure are typically formed on a substrate 10. Thesubstrate 10 may include any structure that has an exposed surface.Structures are preferably those used in the manufacture of semiconductordevices such as silicon wafer, silicon-on insulator (SOI), silicon-onsapphire (SOS), aluminum titanium carbide (AlTiC) doped and undopedsemiconductors, III-V or II-VI semiconductors, epitaxial layers ofsilicon supported by a base semiconductor foundation, and othersemiconductor structures. The semiconductor need not be silicon-based.The semiconductor could be silicon-germanium, germanium, or galliumarsenide. The structure could also be a non-semiconductor such as glassor polymer. The substrate 10 may include buried electronic devices suchas transistors, diodes, capacitors, and resistors, or any other deviceor circuit element that would be used in conjunction with the magneticmultilayer stack.

For the typical multilayer MRAM structure shown in FIG. 1, within whichis contained an MTJ, it is understood that the specific layers. e.g.,materials and their arrangements, that form the multilayer structure canvary. MTJ and MRAM structures are known in the art and are described,for example, in U.S. Pat. No. 6,673,675 to Yates, et al., entitled“Methods of Fabricating an MRAM Device Using Chemical MechanicalPolishing”; U.S. Pat. No. 6,677,165 to Lu, et al., entitled“Magnetoresistive Random Access Memory (MRAM) Cell Patterning”; U.S.Pat. No. 6,653,704 to Gurney, et al., entitled “Magnetic Memory withTunnel Junction Memory Cells and Phase Transition Material forControlling Current to the Cells”; U.S. Pat. No. 6,024,885 toPendharkar, et al., entitled “Process for Patterning Magnetic Films”;and U.S. Pat. No. 5,650,958 to Gallagher, et al., entitled “MagneticTunnel Junctions with Controlled Magnetic Response”; all of which areincorporated herein by reference.

It should be understood that the orientation of the magnetic film stackcan be reversed relative to the order shown in FIG. 1. That is, theorientation of the film structure can be such that the film stack can bedeposited in reverse order with the top contact layer and free magnetlayer are below the dielectric tunnel layer and the multi-layer fixedand antiferromagnetic layers are placed above the dielectric tunnellayer. It should also be understood that the magnetic film stack cancomprise multiple magnetic tunnel junctions in orientations in which thefree layer is deposited above the dielectric tunnel layer or below thedielectric tunnel layer and remain within the scope of the inventivemethod.

In one simplified embodiment shown in FIG. 2, the MTJ stack comprises asubstrate 10, a bottom contact layer 14, a fixed bottom magnet layer 16,a dielectric tunnel layer 18, a switchable upper magnet layer 20, and atop contact layer 22. The stack structure is patterned with photoresistlayer 28. This simplified structure is used in the following descriptionof the preferred embodiments for the present invention.

Inventive etch-stop process sequences are provided in FIGS. 3, 4, and 5.

FIG. 3 shows an inventive process sequence in which the magnetic stackis deposited 100, the PR is patterned 102, one or both of the hard maskand top contact layers are etched 104, and a reactive etch process isused to remove part of the upper magnet layer 106. Following thereactive etch of the upper magnet layer 106, MTJ device structures areexposed to an inventive etch stop process 108 directly, or first to acorrosion treatment sequence consisting of a Dl rinse, a PR strip, and aplasma based corrosion treament, followed by an inventive etch stopprocess 108.

In one embodiment shown in FIG. 3 in which the inventive etch stopprocess 108 directly follows the reactive partial etch of the uppermagnet 106, the patterning of the MTJ device structures is completed andthe devices are moved to subsequent processing 114. In a secondembodiment in which the inventive etch stop process 108 directly followsthe reactive partial etch of the upper magnet 106, the devices areexposed to a sequence of processes to prevent corrosion. Exposure ofmagnetic films to chlorine- and bromine-containing etch chemistries canproduce adverse reactions upon removal of the devices from vacuum andsubsequent exposure of the etched films to moisture under ambientconditions. Depending on the sensitivity of the films, various sequenceshave been developed for preventing adverse corrosive reactions such asthose shown in FIG. 3.

In one embodiment of the inventive process in which corrosion preventiontreatments are employed and in which the corrosion treatments areemployed following the etch stop on the tunnel layer 108, the corrosiontreatment sequence consists of a Dl water rinse 110 followed by aphotoresist strip/corrosion treatment 112. In a second embodiment of theinventive process in which corrosion prevention treatments are employedand in which the corrosion prevention treatments are employed followingthe etch stop on the tunnel layer 108, the corrosion preventiontreatment sequence consists of a photoresist strip/corrosion treatment112, followed by Dl water rinse 110.

In one embodiment shown in FIG. 3 in which the inventive etch stopprocess 108 does not directly follow the reactive partial etch of theupper magnet 106, but rather is preceded by corrosion preventiontreatments 110 and 112. In the first embodiment shown in FIG. 3 in whichthe inventive etch stop process does not directly follow the reactivepartial etch of the upper magnet 106, the MTJ device structures areexposed to a Dl water rinse 110 followed by a photoresiststrip/corrosion treatment 112 prior to the inventive etch stop on thetunnel layer 108. In a second embodiment of the inventive process inwhich the inventive etch stop process 108 does not directly follow thereactive partial etch of the upper magnet 106, the devices are exposedto a photoresist strip/corrosion treatment 112 followed by a Dl waterrinse prior to the inventive etch stop on the tunnel layer 108.

FIG. 4 shows an inventive process sequence in which the magnetic stackis deposited 100, the PR is patterned 102, and the hard mask is etched103. Following the hard mask etch 103, MTJ device structures are exposedto a photoresist strip process 107 or to a reactive etch process 105 toremove the top contact layer and a reactive etch process 106 to removepart of the upper magnet. In a first embodiment of the inventive processin which the hard mask etch process 103 is followed by photoresist stripprocess 107, subsequent to the photoresist process 107 the MTJ devicesare exposed to a reactive etch process 105 to remove the top contactlayer and a reactive etch process 106 to remove part of the uppermagnet. In a second embodiment of the inventive process in which thehard mask etch process 103 is followed by a reactive etch process 105 toremove the top contact layer and a reactive etch process 106 to removepart of the upper magnet, the MTJ devices are subsequently exposed to aphotoresist strip process 107.

Following the combined steps of photoresist strip 107 and reactive etchprocesses 105 to remove the top contact layer and 106 to remove part ofthe upper magnet, the MTJ devices are exposed to the etch stop process108 directly, or first to a corrosion treatment sequence consisting of aDl rinse and a plasma based corrosion treament 113, followed by aninventive etch stop process 108.

In one embodiment shown in FIG. 4 in which the inventive etch stopprocess 108 directly follows the reactive partial etch of the uppermagnet 106, or follows a photoresist strip process 107 that was precededby the reactive partial etch of the upper magnet 106, the patterning ofthe MTJ device structures is completed and the devices are moved tosubsequent processing 114. In a second embodiment in which the inventiveetch stop process 108 directly follows the reactive partial etch of theupper magnet 106, or follows a photoresist strip process 107 that waspreceded by the reactive partial etch of the upper magnet 106, thedevices are exposed to a sequence of processes to prevent corrosion.Exposure of magnetic films to chlorine- and bromine-containing etchchemistries can produce adverse reactions upon removal of the devicesfrom vacuum and subsequent exposure of the etched films to moistureunder ambient conditions. Depending on the sensitivity of the films,various sequences have been developed for preventing adverse corrosivereactions such as those shown in FIG. 4.

In one embodiment of the inventive process in which corrosion preventiontreatments are employed and in which the corrosion treatments areemployed following the etch stop on the tunnel layer 108, the corrosionprevention treatment sequence consists of a Dl water rinse 110 followedby a plasma-based corrosion treatment 112. In a second embodiment of theinventive process in which corrosion prevention treatments are employedand in which the corrosion prevention treatments are employed followingthe etch stop on the tunnel layer 108, the corrosion preventiontreatment sequence consists of a plasma-based corrosion preventiontreatment 112, followed by Dl water rinse 110.

In one embodiment shown in FIG. 4 in which the inventive etch stopprocess 108 does not directly follow the reactive partial etch of theupper magnet 106, but rather is preceded by corrosion preventiontreatments 110 and 113. In the first embodiment shown in FIG. 4 in whichthe inventive etch stop process does not directly follow the reactivepartial etch of the upper magnet 106, the MTJ device structures areexposed to a Dl water rinse 110 followed by a plasma-based corrosiontreatment 113 prior to the inventive etch stop on the tunnel layer 108.In a second embodiment of the inventive process in which the inventiveetch stop process 108 does not directly follow the reactive partial etchof the upper magnet 106, the devices are exposed to a plasma-basedcorrosion treatment 113 followed by a DI water rinse prior to theinventive etch stop on the tunnel layer 108.

Two approaches to the subsequent processing 114, as indicated in FIG. 3and FIG. 4, are shown in FIG. 5 a and FIG. 5 b. These figures describetwo specific methods that specifically exploit the unique capabilityafforded by inventive etch stop process step 108.

In FIG. 5 a, a spacer is used to passivate the sidewall of the MTJdevice structure to prevent electrical shorting during subsequentprocessing. The sidewall spacer is used in conjunction with an etch stopprocess such as that described by etch stop process 108 shown in FIGS. 3and 4. FIG. 5 a shows the preferred embodiment for subsequent processingsteps that follow the inventive etch stop process 108 shown in FIGS. 3and 4. In this preferred embodiment, the subsequent process 114described in FIGS. 3 and 4 consist of a spacer dielectric deposition130, a spacer etch 132, and a bottom magnet/bottom contact etch 134 tocomplete the process or a bottom magnet/bottom contact etch 134 followedby a Dl water rinse step followed by a plasma-based corrosion preventiontreatment 142. Alternatively, the plasma-based corrosion preventiontreatment 142 can precede the Dl water rinse as shown in FIG. 5 a beforeproceeding with subsequent processing of the device 150.

In FIG. 5 b, an alternative approach to subsequent processing 114 isshown in which an insulating hard mask layer such as silicon dioxide orsilicon nitride is deposited 120, photoresist is patterned 122, the hardmask is etched 124, the photoresist is stripped 126, and the bottommagnet and bottom contact are etched 128. In this approach, thephotoresist patterning is such that the silicon dioxide or siliconnitride hard mask layer extends laterally beyond the vertical sidewallproduced from the original hard mask etch 103, upper contact etch 105,reactive upper magnet etch 106, and etch stop process 108. The lateralextension of hard mask 120 beyond the vertical sidewall, uponphotoresist patterning 122, should be such that the sidewall of theoriginal hardmask, the upper contact, and the upper magnet layer remainscovered with hard mask layer 120 after hard mask layer etch 124.

The layers that comprise the MRAM stack or other magnetic devicestructure are deposited 100 using techniques employed by those skilledin the art of film deposition. The films may be deposited by physicalvapor deposition, chemical vapor deposition, atomic layer deposition,nano-layer deposition, atomic layer deposition, evaporation, and othertechniques. The films in the stack may also be deposited by one of thesemethods in one form and subsequently modified in a second chamber. Thealumina (Al₂O₃) dielectric, for example, might be formed by depositing alayer of aluminum and subsequently exposing the aluminum to an oxidizingprocess to form alumina. Similarly, MgO might be formed by depositing alayer of magnesium and subsequently exposing the Mg to an oxidizingprocess to form MgO.

A photoresist deposition and patterning step 102 is used to create apattern for defining the MTJ or MRAM stack. Although not shown in thesimplified MRAM stack example in FIG. 2, an antireflective coating canbe used in conjunction with the photoresist to improve the accuracy ofthe pattern transfer. Additionally, a hard mask layer can beincorporated between the photoresist and the top contact layer. Hardmask layers such as silicon dioxide and silicon nitride could be used.Alternatively, the thickness of the conductive top contact layer can bemade such that it can serve the dual purpose of hard mask and topcontact layer. FIG. 2 shows the simplified MRAM stack structure aftermagnetic stack deposition 100 and subsequent photoresist patterning 102.

In the preferred embodiment, the hard mask layer and the upper contactlayer layers are patterned 103 using common techniques employed by thoseskilled in the art. One example of a common process for reactivelyetching a silicon oxide hard mask, if present, is to use a mixture ofCF₄, CHF₃, and Ar. Oxide etch processes are widely available in theliterature. Similarly, an example of a process chemistry that iscommonly used to reactively etch the top conductor layer 104, 105 is theuse a mixture of Ar/Cl₂. Again, metal contact layer etches have beenpublished extensively in the literature. Oxide and nitride hard masksand metal contact layers have been in use for many years and thetechniques that have been used to remove these layers are apparent tothose skilled in the art. The simplified MRAM stack structure aftercontact etch is shown in FIG. 6.

The removal of the magnetic layers found in a magnetic multi-layerstacks is not well established in the art. Within the scope of thisinvention, is the use of a process that is particularly well-suited forreactive upper magnet layer etch 106 in combination with etch stopprocess 108. This inventive process 106 consists of a gas mixture of achlorine-containing gas such as Cl₂, BCl₃, and HCl and afluorine-containing gas such as CF₄, SF₆, and CHF₃ to remove part of thetop magnet layer. Alternatively, a gas molecule that contains Cl and Fatoms might be used. The ratio of chlorine-containing tofluorine-containing gases should be in the range of 2:1 to 20:1. Typicalprocess conditions for the reactive etch step 106, demonstrated in theSpectra® inductively coupled process module manufactured by TegalCorporation, are as follows: 400 W of 13.56 MHz rf power on theinductive source coil, 20 W of 450 kHz rf power applied to thesubstrate, 40 sccm Cl₂, 8 sccm CF₄, and 4 mT process pressure. Thesimplified MRAM stack structure after reactive magnet layer etch 106 isshown in FIG. 7.

The inclusion of fluorine as an additive to a chlorine-containing etchprocess has been found to produce smooth etched surfaces (as shown inFIG. 8) and prevent diffusion of the chlorine species through very thinfilms of magnetic material that remain after reactive upper magnet etchstep 106. Use of a fluorine/chlorine containing gas mixture allows forremoval of the upper magnet layer to within 5-25 Å of the interfacebetween the remaining upper magnet layer and the underlying dielectrictunnel layer.

In the preferred embodiment of the inventive reactive upper magnet etchprocess 106, the remaining upper magnet layer will be etched as close aspossible to the interface between the remaining upper magnet layer 20and the underlying dielectric layer 18 without penetrating the tunnelingdielectric layer in the vicinity of the features prior to moving to asubsequent processing step such as the etch stop process 108, the Dlwater rinse 110, or the PR strip/corrosion treatment 112. In a preferredembodiment, the upper magnet layer 20 is etched uniformly and theunderlying dielectric layer 18 is not breached anywhere on the waferduring the reactive upper magnet layer etch 106 as shown in FIG. 7.

In one embodiment of the inventive process, however, the upper magnetlayer 20 is completely removed and the underlying dielectric layer 18 isbreached, but not within close proximity of the patterned MTJ stackfeatures (See FIG. 9). In this embodiment of the inventive process, theupper magnet layer etch 106 is removed with an etch process thatcontains one or more of the following gases or gas mixtures: Cl₂,Cl₂/Ar, Cl₂/CF₄, Cl_(2/)CHF₃, Cl_(2/)Ar, BCl₃/Cl₂, BCl_(3/)Cl_(2/)Ar,BCl_(3/)HBr,/Ar, BCl_(3/)HBr/Ar,NH₃, NH₃/CO.

In yet another embodiment, the upper magnet layer 20 is completelyremoved, the underlying dielectric layer 18 is also removed outside of asloped region in close proximity of the patterned MTJ stack, and all orpart of the bottom magnet layer 16 and all or part of the bottom contactlayer 14 are removed. (See FIG. 10.) A unique benefit of this embodimentis that the full MRAM structure is patterned with a single mask;subsequent processing steps 114 are not required. In this embodiment ofthe inventive process, the upper magnet layer etch 106 is removed withan etch process that contains one or more of the following reactivegases and gas mixtures: Cl₂, Cl_(2/)Ar, Cl₂/CF₄, Cl₂/CHF₃, Cl₂/Ar,BCl₃/Cl₂, BCl₃/Cl₂/Ar, BCl₃/HBr, BCl₃/HBr/Ar, NH₃, NH₃/CO.

The remainder of the upper magnet layer that is not removed in thereactive step 106, in the aforementioned embodiments is subsequentlyremoved using etch stop process 108 consisting, in the preferredembodiment, of a mixture of a non-reactive gas such as argon and anoxidizing gas, such as oxygen, whereby the dielectric of the tunnelbarrier layer serves as the stop layer. In the preferred embodiment, theinert gas flow is typically in the range of 10 to 350 sccm and the flowof the oxygen-containing gas is in the range of 0.02 to 0.15 sccm.Actual flows for the oxygen-containing gas can vary depending on theflow of inert gas, the selection of the oxygen-containing gas, and thetype of plasma system used. A typical process 108 used in the Spectra®inductively coupled etch process module manufactured by TegalCorporation is as follows for a 200 mm diameter silicon substrate: 100 Wof 13.56 MHz rf power on the source coil, 20 W of 450 kHz rf powerapplied to the substrate, 350 sccm Ar, 0.08 sccm O₂, and 10 mT processpressure. The conditions provided above for the etch stop, sputterprocess step 108 are intended to provide an exemplary set of conditionsthat have been found to produce a sputter selectivity between NiFe andalumina of ˜90:1 in the Spectra lCP process module manufactured by TegalCorporation. (See FIG. 11.)

A range of process conditions and chamber configurations can be used toproduce results with high selectivity between the upper magnet materialand the dielectric. Two factors that must be considered in achievinghigh selectivity are the control of the ratio of inert gas tooxygen-containing gas in the process chamber and the operation of theprocess at low bias power levels. These two factors are discussed inmore detail in the following paragraphs.

In the preferred embodiments, the etch stop process requires a highselectivity (>5:1) between the upper magnet layer 20 and the underlyingdielectric layer 18. It is expected that the upper magnet layer 20 willbe etched at a rate of at least 5 times faster than the rate at whichthe underlying dielectric layer 18, e.g., Al₂O₃, is etched. Precisecontrol of the NiFe/CoFe etch rate is possible because there aresignificant differences in sputter thresholds between the NiFe and CoFeand that of oxidized metals such as Al₂O₃ and MgO. Experiments thatconfirmed these phenomena were conducted using a Spectra® process modulemanufactured by Tegal Corporation (Petaluma, Calif).

Specifically, NiFe and CoFe sputter rates were measured with monolayertest wafers and alumina etch rates were measured with alumina/NiFe teststructures. The test structure consisted of a substrate that had a NiFelayer deposited thereon and a very thin layer of alumina (˜15Å) over theNiFe. The measured alumina etch rates were representative of the thinfilm properties that would be found in stacks containing magnetictunneling junctions.

As is apparent from the graph in FIG. 12, a significant difference wasobserved between the onset of sputtering for the magnetic alloys incomparison to that of the alumina. It was further observed in etch ratetests, which were performed on alumina/NiFe test structures at biaspower levels greater than 10 W and less than 25 W, that the alumina didnot measurably etch. These observations indicate that under specificprocess conditions, significant amounts of NiFe and CoFe can be etchedfrom a TMR stack while only a small amount of alumina is removed in thesame amount of time.

The resulting device profiles following the preferred embodiments ofreactive etch steps 106 as shown in FIGS. 7, 9, and 10 and etch stopprocess 108 are shown in FIGS. 13, 14, and 15. In each of theseembodiments, the residual metal film that remains of upper magnet layer20 after reactive etch step 106, is removed from the underlyingdielectric layer 18. The removal of the upper magnet layer 20 thatremains after reactive step 106 with a low bias non-reactive etch stop108 provides superior electrical isolation over other known methodswithout damaging the underlying dielectric layer 18. Geometric isolationis provided in each of the three embodiments of the inventive processwithout the inherent risk of electrical shorting that has been known tolimit device performance for structures incorporating MTJ stacks.Superior electrical isolation between the upper magnet layer 20 and thebottom magnet layer 16 is also accomplished with the inventive processwithout the associated risks involved in using corrosive chemistries atthe stage of the process that is most critical for producing reliabledevices.

The typical process conditions for etch stop 108 provided above areintended to be representative of a process that was found to yield anexceptionally high selectivity between NiFe or CoFe and alumina.Variations of the process conditions within the Spectra reactor can beused within the scope of the inventive etch stop process 108.

Similar processes utilizing the approach of either one or both of afirst step of removing the bulk of the upper magnet layer using amixture of chlorine and fluorine containing gases and a second step ofusing a mixture of an inert gas and oxygen-containing gas for stoppingon the dielectric tunneling layer can also be developed in otherinductively coupled plasma reactors, in capacitively-coupled plasmareactors, electron cyclotron resonance reactors, and in other reactorsused to generate plasmas for the purpose of manufacturing devices frommagnetic films and would still be in the scope of the inventive process.Additionally, use of the mixture of an inert gas and anoxygen-containing gas for the purpose of using the dielectric layer asan etch stop without an initial step of using a mixture of chlorine andfluorine containing gases to remove the bulk of the upper magnet layeris also within the scope of the inventive process.

High selectivity in the exemplary embodiment for etch stop 108 describedabove between NiFe and alumina is observed using a gas mixture of argonand oxygen. Within the scope of the inventive process, is the use of oneor both of alternative inert and oxidizing components of the preferredembodiment of the argon/oxygen gas mixture that was used to demonstrateNiFe/alumina selectivity of ˜90:1 in etch stop process 108. Helium,neon, krypton, and nitrogen, for example, can be used in place of, or incombination with argon, to provide the inert component of the etch stopprocess 108. Similarly, alternatives to oxygen such as N₂O, NO, CO, andCO₂, among others, can be used in place of, or in combination withoxygen to produce the oxidizing component of the etch stop process 108.Alternatively, within the scope of the inventive process, theoxygen-containing gas can be eliminated by controlling the oxygen levelin the etch chamber by a method other than the intentional introductionof an oxygen-containing gas as is discussed in the following paragraphs

It has been demonstrated when plasma sputtering magnetic layerscomprising transition metals such as NiFe with inert sputtering gasessuch as Ar, that regulating the amount of oxygen in the plasma chambercan influence the etch selectivity with respect to the underlyingalumina. That is, a higher NiFe/alumina selectivity can be achieved bycontrolling the flow of oxygen into the plasma chamber. One embodimentof the plasma overetch process entails reducing the background oxygen tolevels that do not affect the etching process while concurrentlyre-introducing oxygen in a measurable and controllable manner into theplasma chamber. Sources of the background oxygen that may enter theplasma chamber include, for example: (1) sputtering of oxygen-containinginternal chamber parts, (2) atmospheric oxygen; (3) outgassing frommaterials in the chamber; and (4) other processing modules in theprocess system.

When “uncontrolled” background oxygen in the chamber is reduced, theselectivity between NiFe and alumina can be optimized by re-introducinga very small amount (e.g., ˜0.08 sccm) of oxygen into the chamber. Onetechnique to re-introduce the oxygen employs two separate carrier gassources that are connected to the chamber. The first source supplies anAr/O₂ gas mixture comprising 99.9% Ar and 0.1% O₂ to the plasma chamberwhile a second source supplies a gas containing 100% Ar in parallel tothe chamber. When re-introducing oxygen into the plasma chamber, it ispreferred that the base pressure of the chamber be reduced to ˜0.001 mTor less. Additionally, the sputtering of the surfaces of internalchamber parts should be minimized or controlled. For example, inductivesource power should be low (100-200 W) to minimize window sputtering.Excessive amounts of oxygen in the chamber can slow the etch rate of themetallic magnetic films and can lead to a reduction in selectivitybetween the magnet layers and the dielectric layers.

Alternatively, in a second technique, oxygen is introduced into theprocess chamber through an orifice separating a source of oxygen and theprocess chamber. The orifice is sized such that the flow of the oxygencontaining gas, when mixed with an inert gas, produces an enhancement inthe sputtering selectivity between the upper magnetic film and thetunneling dielectric.

Other means for introducing a controlled level of oxygen into an inertgas to provide the necessary conditions for selectively etching themagnetic material over the dielectric layer can also be used within thescope of this patent. In such embodiments, sputtering of interiorsurfaces of oxygen-containing materials in the plasma reactor can beused as a source of oxygen. In this embodiment, an inert gas such asargon would be introduced through conventional means, such as a massflow controller or needle valve, at such a volume so as to produce amixture of inert gas and oxygen-containing species at the surface of theupper magnetic layer being etched, so as to produce selective removalbetween the magnetic material and the tunneling dielectric layer. Theprocess conditions would be adjusted such that the magnetic materialwould be removed at a rate of >5 Å/min and the dielectric layer would beremoved at a rate of <1 Å/min.

In another embodiment of this invention, the level of anoxygen-containing gas is provided by controlling the leakage ofatmospheric gases into the vacuum chamber. Plasma-based semiconductorfabrication processes are typically performed in the range of 0.1 to1000 milliTorr. In these sub-atmospheric conditions, oxygen can beintroduced inadvertently through imperfect seals, through porousmaterials, and from outgassing of parts in the processing chamber. Therate of leakage can easily be measured in conventional plasma processingequipment.

In this embodiment, an inert gas such as argon would be introducedthrough conventional means, such as a mass flow controller or needlevalve, at such a volume so as to produce a mixture of inert gas andoxygen-containing species at the surface of the upper magnetic layerbeing etched, so as to produce selective removal between the magneticmaterial and the tunneling dielectric layer. Within the scope of thisinvention is the approach of controlling the oxygen-containing leakagefrom atmosphere, in combination with the introduction of controlledinert gas flow through conventional means to produce the requiredmixture of inert gas and oxygen-containing species to the extent thatthe magnetic material is removed at a rate of >5 Å/min and thedielectric layer is removed at a rate of <1 Å/min.

The process for removing the photoresist and preventing corrosion,namely 112 in FIG. 3, 113 in FIG. 4, 142 in FIG. 5 a, and 126 and 142 inFIG. 5 b must be compatible with magnetic film structures. Within thescope of this present invention is the use of hydrogen-containing gasmixtures that are suitable for resist removal and for preventingcorrosion that could result from exposure of the MRAM film stack to thehalogen-containing etch chemistries. In the preferred embodiments, themagnetic film stack is exposed to a hydrogen-containing plasma to removethe photoresist, to expose the magnetic layers to a process that wouldprevent corrosion upon exposure to ambient conditions, or both. Hydrogenis introduced into the process chamber in a mixture of hydrogen and aninert gas such as helium, neon, argon, or nitrogen.

1. A process for fabricating a magnetic junction memory devicecomprising: (a) providing a substrate; (b) forming an insulating layerover the substrate; (c) forming a top metal layer over the insulatinglayer; and (d) applying a non-reactive gas and a bias to the substratewith bias power between the sputter threshold of the top metal layer andthe insulating layer to selectively remove the top metal layer withrespect to the underlying insulating layer.
 2. A process as in claim 1wherein the non-reactive gas is Ar, He, Ne, Kr, N₂, or Xe, or anycombination thereof.
 3. A process as in claim 1 further comprising thestep of forming a bottom metal layer under the insulating layer.
 4. Aprocess as in claim 1 wherein a plasma is formed with the non-reactivegas.
 5. A process as in claim 1 wherein the insulating layer comprisesaluminum oxide, magnesium oxide, or any insulating oxide.
 6. A processas in claim 1 wherein the top metal layer comprises a magnetic layer,part of an MRAM stack structure, or one or more layers of NiFe, CoFe,CoNiFe, and CoFeB.
 7. A process for fabricating a magnetic junctionmemory device comprising: (a) providing a substrate; (b) forming aninsulating layer over the substrate; (c) forming a top layer over theinsulating layer; and (d) applying a physical sputter etch process usinga mixture of a non-reactive gas and <1% of an oxygen-containing gas toselectively remove the top layer with respect to the underlyinginsulating layer, wherein the oxygen-containing gas is introduced intothe process from the sputtering of a solid source of anoxygen-containing solid, and wherein the solid source comprises aluminaor quartz.
 8. A process as in claim 7 wherein the non-reactive gas isAr, He, Ne, Kr, N₂, or Xe, or any combination thereof.
 9. A process asin claim 7 wherein the oxygen-containing gas is O, O₂, N₂O, NO, air, CO,or any combination thereof.
 10. A process as in claim 7 wherein themixture is 99.9% Ar and 0.1% O₂.
 11. A process as in claim 7 wherein themixture of a non-reactive gas and an oxygen-containing gas is introducedthrough a first flow controller and a non-reactive gas is introducedthrough a second flow controller.
 12. A process as in claim 7 whereinthe first flow controller provides 80 sccm of argon and 0.08 sccm of O2and the second flow controller provides 270 sccm of argon.
 13. A processas in claim 7 wherein the non-reactive gas is in the range of 10 to 350sccm and the oxygen-containing gas is in the range of 0.02 to 0.15 sccm.14. A process as in claim 7 wherein the oxygen-containing gas isintroduced from controlled leakage.
 15. A process as in claim 7 furthercomprising the step of forming a bottom metal layer under the insulatinglayer.
 16. A process as in claim 7 wherein a plasma is formed with thenon-reactive gas.
 17. A process as in claim 7 wherein the insulatinglayer comprises aluminum oxide, magnesium oxide, or any insulatingoxide.
 18. A process as in claim 7 wherein the top layer comprises amagnetic layer, part of an MRAM stack structure, or one or more layersof NiFe, CoFe, CoNiFe, and CoFeB.
 19. A process for fabricating amagnetic junction memory device comprising: (a) providing a substrate;(b) forming an insulating layer over the substrate; (c) forming a topmetal layer over the insulating layer; and (d) applying a physicalsputter etch process using a mixture of a non-reactive gas and <1% of anoxygen-containing gas and a bias to the substrate with bias powerbetween the sputter threshold of the top metal layer and the insulatinglayer to selectively remove the top metal layer with respect to theunderlying insulating layer.
 20. A process as in claim 19 wherein thenon-reactive gas is Ar, He, Ne, Kr, N₂, or Xe, or any combinationthereof.
 21. A process as in claim 19 wherein the oxygen-containing gasis O, O₂, N₂O, NO, air, CO, or any combination thereof.
 22. A process asin claim 19 wherein the mixture is 99.9% Ar and 0.1% O₂.
 23. A processas in claim 19 wherein the mixture of a non-reactive gas and anoxygen-containing gas is introduced through a first flow controller anda non-reactive gas is introduced through a second flow controller.
 24. Aprocess as in claim 19 wherein the first flow controller provides 80sccm of argon and 0.08 sccm of O₂ and the second flow controllerprovides 270 sccm of argon.
 25. A process as in claim 19 wherein thenon-reactive gas is in the range of 10 to 350 sccm and theoxygen-containing gas is in the range of 0.02 to 0.15 sccm.
 26. Aprocess as in claim 19 wherein the oxygen-containing gas is introducedinto the process from the sputtering of a solid source of anoxygen-containing solid.
 27. A process as in claim 26 wherein the solidsource comprises alumina or quartz.
 28. A process as in claim 19 whereinthe oxygen-containing gas is introduced from controlled leakage.
 29. Aprocess as in claim 19 further comprising the step of forming a bottommetal layer under the insulating layer.
 30. A process as in claim 19wherein a plasma is formed with the non-reactive gas.
 31. A process asin claim 19 wherein the insulating layer comprises aluminum oxide,magnesium oxide, or any insulating oxide.
 32. A process as in claim 19wherein the top metal layer comprises a magnetic layer, part of an MRAMstack structure, or one or more layers of NiFe, CoFe, CoNiFe, and CoFeB.33. A process for fabricating a device comprising: (a) providing asubstrate; (b) forming an insulating layer over the substrate; (c)forming a top metal layer over the insulating layer; and (d) applying abias to the substrate with bias power between the sputter threshold ofthe top metal layer and the insulating layer to selectively remove thetop metal layer with respect to the underlying insulating layer.
 34. Aprocess as in claim 33 wherein the insulating layer comprises aninsulating oxide.
 35. A process for fabricating a device comprising: (a)providing a substrate; (b) forming an insulating layer over thesubstrate; (c) forming a top metal layer over the insulating layer; and(d) applying a physical sputter etch process using a mixture of anon-reactive gas and <1 of an oxygen-containing gas and a bias to thesubstrate with bias power between the sputter threshold of the top metallayer and the insulating layer to selectively remove the top metal layerwith respect to the underlying insulating layer.
 36. A process forfabricating a magnetic junction memory device comprising: (a) receivinga substrate in a process chamber; (b) forming an insulating layer overthe substrate; (c) forming a top metal layer over the insulating layer;and (d) introducing a non-reactive gas to the process chamber; (e)applying a bias to the substrate with bias power between the sputterthreshold of the top metal layer and the insulating layer to selectivelyremove the top metal layer with respect to the underlying insulatinglayer.
 37. A process as in claim 36 wherein the non-reactive gasincludes one or more of Ar, He, Ne, Kr, N₂, and Xe.
 38. A process as inclaim 36 further comprising the step of forming a bottom metal layerbetween the substrate and the insulating layer.
 39. A process as inclaim 36 wherein a plasma is formed with the non-reactive gas.
 40. Aprocess as in claim 36 wherein the insulating layer comprises aluminumoxide, magnesium oxide, or any insulating oxide.
 41. A process as inclaim 36 wherein the top metal layer comprises a magnetic layer, part ofan MRAM stack structure, or one or more layers of NiFe, CoFe, CoNiFe,and CoFeB.
 42. A process for fabricating a magnetic junction memorydevice comprising: (a) receiving a substrate in a process chamber; (b)forming an insulating layer over the substrate; (c) forming a top metallayer over the insulating layer; (d) introducing a non-reactive gas tothe process chamber; (e) introducing an oxygen-containing gas to theprocess chamber by sputtering one or both of alumina and quartz so thata mixture of non-reactive gas and <1% oxygen-containing gas is formed inthe process chamber; and (d) applying a physical sputter etch process toremove the top metal layer with respect to the underlying insulatinglayer.
 43. A process as in claim 42 wherein the non-reactive gasincludes one or more of Ar, He, Ne, Kr, N₂, and Xe.
 44. A process as inclaim 42 wherein the oxygen-containing gas is O, O₂, N₂O, NO, air, CO,or any combination thereof.
 45. A process as in claim 42 wherein themixture is 99.9% Ar and 0.1% O₂.
 46. A process as in claim 42 furthercomprising the step of forming a bottom metal layer under the insulatinglayer.
 47. A process as in claim 42 wherein a plasma is formed with thenon-reactive gas.
 48. A process as in claim 42 wherein the insulatinglayer comprises aluminum oxide, magnesium oxide, or any insulatingoxide.
 49. A process as in claim 42 wherein the top metal layercomprises a magnetic layer, part of an MRAM stack structure, or one ormore layers of NiFe, CoFe, CoNiFe, and CoFeB.
 50. A process forfabricating a magnetic junction memory device comprising: (a) receivinga substrate in a process chamber; (b) forming an insulating layer overthe substrate; (c) forming a top metal layer over the insulating layer;and (d) introducing a mixture of a non-reactive gas and <1% of anoxygen-containing gas to the process chamber; (e) applying a bias to thesubstrate with bias power between the sputter threshold of the top metallayer and the insulating layer to selectively remove the top metal layerwith respect to the underlying insulating layer.
 51. A process as inclaim 50 wherein the non-reactive gas is one or more of Ar, He, Ne, Kr,N₂, and Xe.
 52. A process as in claim 50 wherein the oxygen-containinggas is O, O₂, N₂O, NO, air, CO, or any combination thereof.
 53. Aprocess as in claim 50 wherein the mixture is 99.9% Ar and 0.1% O₂. 54.A process as in claim 50 wherein introducing the mixture includesintroducing a first portion of the non-reactive gas mixed with theoxygen-containing gas through a first flow controller and introducing asecond portion of non-reactive gas through a second flow controller. 55.A process as in claim 50 wherein the first flow controller provides 80sccm of argon and 0.08 sccm of O₂ and the second flow controllerprovides 270 sccm of argon.
 56. A process as in claim 50 wherein thenon-reactive gas is in the range of 10 to 350 sccm and theoxygen-containing gas is in the range of 0.02 to 0.15 sccm.
 57. Aprocess as in claim 50 wherein the oxygen-containing gas is introducedinto the process from the sputtering of a solid source of anoxygen-containing solid.
 58. A process as in claim 57 wherein the solidsource comprises alumina or quartz.
 59. A process as in claim 57 whereinthe solid source is a consumable component of the process chamber.
 60. Aprocess as in claim 50 wherein the oxygen-containing gas is introducedfrom controlled leakage into the process chamber.
 61. A process as inclaim 50 further comprising the step of forming a bottom metal layerunder the insulating layer.
 62. A process as in claim 50 wherein aplasma is formed with the non-reactive gas.
 63. A process as in claim 50wherein the insulating layer comprises aluminum oxide, magnesium oxide,or any insulating oxide.
 64. A process as in claim 50 wherein the topmetal layer comprises a magnetic layer, part of an MRAM stack structure,or one or more layers of NiFe, CoFe, CoNiFe, and CoFeB.